Table of Contents




ITU-T specification, based on Q.931, for establishing, maintaining, and clearing network connections at the B-ISDN user-network interface. The UNI 3.1 specification is based on Q.2931. See also Q.931 and UNI.


ITU-T specifications for the ISDN UNI data link layer. See also UNI.


ITU-T specification for Frame Relay encapsulation.


ITU-T specification for signaling to establish, maintain, and clear ISDN network connections. See also Q.93B.


ITU standard that describes ISDN signaling. The H.225.0 standard uses a variant of Q.931 to establish and disconnect H.323 sessions.


ITU-T specification for signaling to establish, maintain, and clear BISDN network connections. An evolution of ITU-T recommendation Q.931. See also Q.931.


quadrature amplitude modulation. Method of modulating digital signals onto a radio-frequency carrier signal involving both amplitude and phase coding. QAM is a modulation scheme mostly used in the downstream direction (QAM-64, QAM-256). QAM-16 is expected to be usable in the upstream direction. Numbers indicate number of code points per symbol. The QAM rate or the number of points in the QAM constellation can be computed by 2 raised to the power of <number of bits/symbol>.


Qualified Logical Link Control. Data link layer protocol defined by IBM that allows SNA data to be transported across X.25 networks.


quality of service. Measure of performance for a transmission system that reflects its transmission quality and service availability.

QoS parameters

quality of service parameters. Parameters that control the amount of traffic the source in an ATM network sends over an SVC. If any switch along the path cannot accommodate the requested QoS parameters, the request is rejected, and a rejection message is forwarded back to the originator of the request.


Quadrature Phase-Shift Keying: a method of modulating digital signals onto a radio-frequency carrier signal using four phase states to code two digital bits.


quasi-random signal sequence: a test pattern widely used to simulate voice signals.


Q (point of the ISDN model) Signaling. Signaling standard. Common channel signaling protocol based on ISDN Q.931 standards and used by many digital PBXs.

Qualified Logical Link Control


quality of service

See QoS.

quartet signaling

Signaling technique used in 100VG-AnyLAN networks that allows data transmission at 100 Mbps over four pairs of UTP cable at the same frequencies used in 10BaseT networks. See also 100VG-AnyLAN.


Message used to inquire about the value of some variable or set of variables.


1. Generally, an ordered list of elements waiting to be processed.

2. In routing, a backlog of packets waiting to be forwarded over a router interface.

queuing delay

Amount of time that data must wait before it can be transmitted onto a statistically multiplexed physical circuit.

queuing theory

Scientific principles governing the formation or lack of formation of congestion on a network or at an interface.


Pioneering software package developed to study the OSI Directory and provide extensive pilot capabilities.


query with permission.

Posted: Tue Sep 21 15:22:35 PDT 1999
Copyright 1989-1999©Cisco Systems Inc.